93 Burb 5.7 4x4 W/4l60e Trans, Need Help!!

I Bought This Burb With A Slow Shifting Transmission, It Went Out, Changed With A Good Used One, It Lasted 2 Months, It Lost Drive& Overdrive, Swapped With A Good Used One, It Has No Drive Or Overdrive Either, I Am Trying To Figure Out What Else It Could Be, Surely Not The Tranny, It Worked Fine In The Other Vehicle. Please Help.

If fluid is in these units and they they won't move, the trans is bad or the convertor is bad I assume it won't move at all, or just reverse.